THE HEART 93 



and again register the volumetric changes of the heart. Occlude the 

 venae cavse for a few moments. Explain the result. Withdraw the 

 ventricles from the cardiometer and allow the heart to recuperate. If 

 necessary, cover it for a time with cotton moistened with warmed saline 

 solution. 



Again record the volume-curve of the ventricles. Temporarily 

 obstruct the arch of the aorta. Explain the result. Allow the heart to 

 rest. 



2. Heart-block. Fibrillation. Procure a clamp such as is represented 

 in Fig. 58. Remove the loose connective tissue from the wall of the 

 aorta along a line forming the right edge of the mass of fat which covers 

 the anterior aspect of this blood-vessel. Set the point of the hook in 

 this place, corresponding to the tip of the membranous septum of the 

 ventricles. Direct the needle obliquely downward and toward the 

 lumen of the aorta and force it into the left ventricle, approximately at 

 the junction of the right and posterior flaps of the mitral valve. Turn 

 the point of the hook backward, so that the short arm of the L-shaped 

 clamp comes to lie parallel to the ventricular septum. Now, move the 

 bar until it lies parallel to the first part of the arch of the aorta and 

 force the short arm of the hook into the septum at a point about 3 to 

 6 mm. below the auriculo ventricular junction and somewhat posterior 

 to the mesial flap of the mitral valve. Do not include the main trunk 

 of the coronary artery in the clamp. Tighten the clamp sufficiently 

 to cause a partial block. Not every auricular contraction will then be 

 followed by a ventricular contraction. This condition simulates the 

 condition of heart-block in man, usually brought about by inflammatory 

 lesions along the course of the bundle of His. 



If done in an improper manner, the ventricle will immediately be 

 thrown into a condition of fibrillation. Its musculature then executes 

 irregular wave-like contractions. This condition may also be pro- 

 duced by injections of strophanthin (about 0.0003 gram) . Shortly before 

 the onset of the fibrillation the heart frequently shows a typical block. 



